My Supro has a noisy hum

Mike Bonnice · Post by **Mike Bonnice** » 31 Jul 2008 7:30 pm

I just got a Supro lap steel with the string-through pickup, S/N V9665. It has the loudest idle hum of any guitar ever. When it's plugged in to an amp, the hum is irritating. When I touch the strings, it mostly goes away. The problem is that I intend to perform with this, and I can't have my hands on it at all times, so it needs to be quieter, like any other guitar. What can I do? Anything?

I had a guitar shop replace the cable and the pots since the tone pot dropped out completely and the volume pot was irregular. The cable is wired directly, no jack. I showed the technician the hum, he agrees that it is loud, but assures me that everything is wired correctly inside ("just like any electric guitar") I like the range of sounds I can get out of the pots, but at some nice settings the hum is too loud, so I dial the pots to get acceptable volume with minimum hum.

Any ideas what to do?

Fred Kinbom · Post by **Fred Kinbom** » 1 Aug 2008 1:32 am

This is a funny but working solution I once applied at a gig - the steel was connected to a tremolo pedal, and to "ground" it I took off my shoe and sock off one foot and put my bare foot on the metal pedal. No hum.

I also find that vintage lap steels can hum in some locations and not in others, I guess depending on varying electrical fields. One of my old National New Yorkers get a loud buzz from the computer monitor, for instance.

Fred

Mark MacKenzie · Post by **Mark MacKenzie** » 1 Aug 2008 3:43 am

Sounds like the strings aren't grounded. Is it well shielded? They have copper tape or even conductive paint to shield inside the guitar.

I have a National Electric Hawaiian which is all metal body which works as a complete shield. Even though it is a single coil, there is absolutely no hum.

John Burton · Post by **John Burton** » 1 Aug 2008 4:36 am

If the hum goes away when you touch the strings, it simply isn't grounded right.
I'm not familar with your Supro, but on most guitars: Make sure theres a good ground wire making contact to the bridge.
An Ohm meter would tell you right quick if the strings are grounded. Check between the strings and maybe the post or nut to one of the pots.

Peter Jacobs · Post by **Peter Jacobs** » 1 Aug 2008 4:52 am

My Supro Jet Airliner has a string through pickup, and it's unbelievably quiet. I agree with Mark and John -- assuming you don't have this hum problem with your other lap steels (which might mean it's your house, not your steels -- believe me, I have too much experience with this), it's most likely a grounding issue. The string through pickup is humbucking by design.

Are the pots on a separate plate, or on the same plate as the pickup? If they are separate, there's a wire missing somewhere, probably from the back of a pot to the pickup/bridge plate.

Peter

Tom Pettingill · Post by **Tom Pettingill** » 1 Aug 2008 9:43 am

Yea, most likely a grounding issue

Rick Aiello · Post by **Rick Aiello** » 1 Aug 2008 12:43 pm

Mike Bonnice wrote: When I touch the strings, it mostly goes away.

but assures me that everything is wired correctly inside ("just like any electric guitar") I like the range of sounds I can get out of the pots, but at some nice settings the hum is too loud, so I dial the pots to get acceptable volume with minimum hum.

Any ideas what to do?

The units that folks have sent me to work on ... had the coils ... ground to the metal base plate.

Everything can appear to be properly grounded on inspection ... but a failure at that specific point ... IE. the coil grounding to the plate ... can/will go undetected ...

If you exhaust all possibilities ... then its time to send the pup to Jason Lollar ... http://www.lollarguitars.com/Winding.htm

As stated above, the string thru units are very quiet ... when fully functional.

Peter Jacobs wrote:The string through pickup is humbucking by design.

With all due respect ... they are split single coils ...

Some of the oldest had 6 individual coils ... most have two coils that are off set.

To be humbucking ... a pickup must have coils that are reverse wound and each coil's magnet(s) must be reverse in polarity.

Rick Alexander · Post by **Rick Alexander** » 1 Aug 2008 1:45 pm

Rick Aiello wrote: Some of the oldest had 6 individual coils ...

I found one of those on eBay a few years ago.

It needed a little work . .

But it's alright now . .

Craig Prior · Post by **Craig Prior** » 1 Aug 2008 2:21 pm

Fred Kinbom wrote:... to "ground" it I took off my shoe and sock off one foot and put my bare foot on the metal pedal. No hum.

Fred, I'm sure you're aware of this, but on a cement floor (that particular floor appeared to be wood) this is a good way to shock the bejesus outta yourself.

Mike Bonnice · Post by **Mike Bonnice** » 1 Aug 2008 10:45 pm

I took everything apart and found the noise came from the cable. The hum was still there when I desoldered the cable from the pot. I had another guitar cable that was quiet when plugged in to the amp, so I cut an end off and soldered it to the pot.

Maybe the cable is too long, because I think I lost some volume. Does this happen? Should I try a shorter cable? The Supro does not have a jack, and unless I want to mess up the body with a new hole I don't think I can fit a jack. Is it possible to find a cable with a female end?

Anyway, the hum is gone.

By the way, as I was disassembling the pickup to see if anything was amiss, I broke one of the pole piece screws. These are the slotted screws that can be screwed in or out through the holes in the top of the pickup. It was so tight that when I turned it the slot stripped. To fix it, I turned the screw out using a vise grip on the end protruding through the bottom, then I chased the threads and cut a new slot on the other end of the screw with a Dremel cut-off wheel. Now it's fine!

I tried replacing the pole piece screws with #6-32 stainless steel cap-head screws from Home Depot, but the pickup became mute. I think that material doesn't work as a pole piece.

Jim Mitchell · Post by **Jim Mitchell** » 2 Aug 2008 7:44 am

Rick,

That is the first time I have ever seen Roman Numerals on a guitar.

Was that common back then?

I am going to build me a lap steel in the fall when I get my garage built
And my wood shop set up again.

I have some wild cheery wood stored I may try.

I think I am going to use that type of fret board

“With your permission of course”

MY SITE
http://www.geocities.com/insp/SUPRO6420.html

Fred Kinbom · Post by **Fred Kinbom** » 2 Aug 2008 8:03 am

Jim Mitchell wrote:That is the first time I have ever seen Roman Numerals on a guitar.

Was that common back then?

That's two 1937 National New Yorkers. IMHO these Roman numbers (in parallellograms - also used on some National Tricones in the late 1930s) look even better than the subsequent design as on Rick's early 1940s Chicagoan (?) and the later New Yorkers.

Fred

Rick Aiello · Post by **Rick Aiello** » 2 Aug 2008 8:48 am

Mike Bonnice wrote: I tried replacing the pole piece screws with #6-32 stainless steel cap-head screws from Home Depot, but the pickup became mute. I think that material doesn't work as a pole piece.

They have to be ferromagnetic ...

The stainless screws you purchased ... were probably non-magnetic 300 series stainless ...

Just get steel (zinc plated) screws ... and you'll be good to go ...

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My Supro has a noisy hum

My Supro has a noisy hum

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